Google Books

Google Books is a service from Google that searches the full text of books that Google has scanned, converted to text using optical character recognition (OCR) technology, and stored in a digital format. Results from Google Book Search show up in both general web search at google.com and through the dedicated Google Books site (books.google.com). Up to three results from the Google Books index may be displayed, if relevant, above other search results in the Google Web search service (google.com).
You must have a gmail address in order to use the service. Subscribing users can click on a result from Google Books that opens an interface in which the user may view pages from the book, if out of copyright or if the copyright owner has given permission. Books in the public domain are available in "full view" and free for download. For in print books, Google limits the number of viewable pages through a variety of access limitations and security measures, some based on user-tracking.
For books that may be covered by copyright and where the owner has not been identified, only "snippets" (two to three lines of the text) are shown, though the full text of the book is searchable. You may create yourself a Bookshelf (in digital format) and download any book that is not protected by copyright.

Click here to learn how the service works.